The manufacture of products such as disposable absorbent articles involves the use of flexible materials. The flexible materials can include, by way of illustration, non-woven materials, elastic materials, adhesive tapes, polymeric films, release paper, mechanical fastening materials, paper webs, and the like. During the formation of products, these materials are typically unwound from relatively large rolls of material and fed into a process where the material is manipulated, possibly combined with other materials, and formed into products.
When feeding a roll of material into a process, typical unwind systems may include an unwind device that is configured to hold a roll of material and to unwind the material. Such systems can also include a splicing device, a festoon, and a dancer roll.
The splicing device is for splicing a first material to a second material when the roll containing the first material is exhausted and needs to be replaced by a second full roll of material.
The basic purpose of a dancer roll is to feed the material into a process under substantially constant tension. Dancer rolls are typically positioned between two sets of driving rolls. As the material passes over the dancer roll, the dancer roll moves up and down in a track, serving two functions related to stabilizing the tension in the material. First, the dancer roll provides a tensioning force to the material. Second, the dancer roll temporarily absorbs the difference in drive speeds between the first and second sets of driving rolls. Dancer rolls are described in detail in U.S. Pat. No. 6,473,669 to Rajala et al., which is incorporated herein by reference.
Festoons, which may be placed in between the unwind device and the dancer roll, are designed to accumulate and temporarily hold a limited length of the material. The accumulated material is then released or additional length is accumulated when processing of the continuous material is temporarily interrupted. Such temporary interruptions can be, for example, when splicing a first material to a second material.
Festoons can include, for instance, a row of top idler rolls spaced from a row of bottom idler rolls. The top idler rolls are connected to a carriage that allows the rolls to move towards and away from the bottom idler rolls. The material is threaded through the festoon by passing back and forth between the bottom idler rolls and the top idler rolls. In this manner, the festoon is capable of accumulating the needed amount of material. In order to release the material, the top idler rolls move towards the bottom idler rolls decreasing the amount of material held in the festoon. Likewise, in order to increase the capacity of the festoon, the top idler rolls may move away from the bottom idler rolls.
During, for instance, a splice operation, a first roll of material is decreased in speed from the process speed to a slower speed or even stopped. Once the speed of the web is lowered, a splicing device splices a second roll of material to the first roll of material. During this time, material accumulated in the festoon continues to feed material into the process without interruption. The second roll of material is then accelerated to a rate greater than the process speed in order to re-supply the festoon. Once the festoon has accumulated a sufficient amount of material, the unwind speed of the second roll of material is decreased to the process speed.
During the above splicing operation, the idler rolls contained in the festoon are accelerated and decelerated in conjunction with the rate at which the material is unwound. In the past, material tension on the idler rolls was used to decelerate and accelerate the rolls. Consequently, the rolls were made with a low mass and low inertia.
As the need for higher process speeds increases, however, the festoon capacity required to make splices or account for other interruptions becomes prohibitably high. Further, materials are being made with very low moduli of elasticity which may become damaged or break should the material be subjected to moderate increases in tension during interruptions. As such, a need currently exists for an improved system of unwinding a roll of material that reduces the amount of festoon capacity required and which minimizes tension swings in the festoon during interruptions.